Electromagnetic fluctuation properties in C-2W Field-Reversed Configuration (FRC) hydrogen and deuterium plasmas

In the C-2W Field Reversed Configuration (FRC), comparisons of transport-relevant fluctuation properties in hydrogen and deuterium plasmas indicate significant differences in radial correlation length, skewness, toroidal magnetic field fluctuation amplitude, as well as cross-correlation between ñ and b~. These measurements are made via multi-channel Doppler Backscattering (DBS) and Cross Polarization Scattering (CPS) techniques, accessing a toroidal wavenumber range 0.5 ≤ k_θρ_s ≤ 5. In a comparison of C-2W mirror and FRC plasmas, increased magnetic fluctuation levels were observed in the FRC configuration, along with anti-correlation of ñ and b~, consistent with the high normalized FRC kinetic pressure (<β> ~1). Radial transport barrier formation in both hydrogen and deuterium plasmas maintains a core plasma state characterized by very low ion-scale fluctuation levels [1] in agreement with global gyrokinetic simulations [2]. We present here also an 8 channel DBS/CPS system design for the planned Copernicus FRC device.

[1] L. Schmitz et al., Nature Comm. 7 13860 (2016).

[2] C. Lau et al., Nucl. Fusion 59 066018 (2019).